We have collaborated with epidemiologists and industrial hygienists in the Occupational Studies Branch to examine a variety of occupational exposures. Benzene is widely used in manufacturing and is a contaminant of many solvents. Although benzene has been identified as a cause of acute myeloid leukemia since 1981, we designed a large study to provide information on risks at low exposures and on the range of hematopoietic conditions associated with benzene exposure. We studied a cohort study of more than 75,000 benzene-exposed and 35,000 unexposed workers from 12 cities in China. A nested case-control study of hematopoietic malignant and related benign conditions provided further medical detail for 94 cases and 382 controls. A detailed clinicopathologic review of all incident hematopoietic conditions revealed excesses of non-Hodgkin's lymphoma, myelodysplastic syndromes (preleukemias), aplastic anemia, and acute lymphoblastic leukemia, in addition to acute myeloid leukemias. The median total white blood counts of benzene-exposed workers who developed these hematopoietic disorders were notably lower than those of unexposed workers who developed such disorders. Lung cancer risk was linked to increased cumulative exposure. Preliminary analyses revealed excess risks for all hematopoietic and related disorders at exposure concentrations less than 10 parts per million (ppm) and at 40 ppm-years of cumulative exposure. While risk for non-Hodgkin's lymphoma rose with increasing duration of exposure, risks associated with development of acute myeloid leukemia and myelodysplastic syndromes were linked with rising average exposure levels and recent exposures, but not with duration of exposure. Biomarker studies among 44 currently exposed workers demonstrated depressed lymphocyte levels, which may be related to our findings of excesses of non-Hodgkin's lymphoma and acute lymphoblastic leukemia. We have also initiated studies to link data on occupation from 1960 and 1970 with cancer incidence from 1971-1989 using National Swedish Cancer Registries. Preliminary analyses have confirmed a gradient of increasing colon cancer risk among sedentary occupations.